In general, a liquid crystal display (LCD) device controls the light transmittance of liquid crystal cells in response to video signals. In this way a picture is displayed that corresponds to the video signals on a liquid crystal display panel. To this end, the LCD device includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix, and driving circuits for driving the liquid crystal display panel.
FIG. 1 is a sectional view illustrating a related art liquid crystal display panel.
Referring to FIG. 1, the liquid crystal display panel includes a color filter array substrate having a black matrix 4, a color filter 6, a common electrode 10, and an upper alignment layer 12, which are sequentially formed on an upper glass 2. A thin film transistor array substrate having a thin film transistor (TFT), a pixel electrode 16, and a lower alignment layer 42 are formed on a lower glass 32. A liquid crystal material (not shown) resides in an inner space between the color array substrate and the thin film transistor array substrate.
In the color filter array substrate, the black matrix 4 is formed on the upper glass 2 so as to correspond to the area of the TFT and the area (not shown) of gate and data lines in the thin film transistor array substrate. The black matrix 4 also partitions the cell regions at which the color filter 6 is to be formed. The black matrix 4 serves to prevent light leakage and to absorb external light, thereby improving the contrast ratio. The color filter 6 is formed over the cell region partitioned by the black matrix 4. The color filter 6 is formed by separate red (R), green (G), and blue (B) filters and represents red, green, and blue colors. A common reference voltage that drives the liquid crystal material is applied to the common electrode 10. A spacer (not shown) maintains a cell gap between the color filter array substrate and the thin film transistor array substrate.
In the thin film transistor array substrate, the TFT includes a gate electrode 38 formed on the lower glass 32 along with a gate line (not shown). Semiconductor layers 14 and 48 overlap the gate electrode 38 with a gate insulating layer 34 positioned therebetween. Source and drain electrodes 68 and 70 along with a data line (not shown) overlie the semiconductor layers 14 and 48. The TFT supplies pixel signals from the data line to the pixel electrode 16 in response to scan signals from the gate line.
The pixel electrode 16 is made of a transparent conductive material with a high light transmittance and overlies a passivation film 50 and contacts the drain electrode 70 of the TFT. After an alignment material, such as a polyimide, is applied to the upper substrate and the lower substrate, a rubbing process is performed, to form the upper/lower alignment films 12 and 42 for aligning the liquid crystal material.
The liquid crystal display panel having the above-mentioned arrangement is shown in FIG. 2. The display panel includes an upper mother glass 1 of a large size having an array region P1 and a dummy region P2. A plurality of color filter arrays 80 reside in the array region P1. A separate lower mother glass (not shown) includes a plurality of thin film transistor arrays in an array region of the lower mother glass. After forming the color filter arrays and the thin film transistor arrays, the upper and lower mother glasses are combined. Hence, a plurality of the liquid crystal display panels is simultaneously formed, to thereby promote an improvement of a production yield. Herein, the dummy region P2 of the upper mother glass 1 partitions each of the color filter arrays 80.
FIGS. 3A to 3C illustrate sequential process steps for forming a plurality of color filter arrays on the related art upper mother glass.
First, a black matrix material, for example, chrome (Cr), is deposited on the upper mother glass 1. Then, the black matrix material is patterned by a photolithography and etching process to form the black matrix 4 at the array region P1 of the upper mother glass 1, as shown in FIG. 3A.
A red resin is deposited on the upper mother glass 1 having the black matrix 4 formed thereon. Then, the red resin is patterned by way of a photolithography and etching process. Consequently, a red color filter R is formed at the array region P1. A green resin is deposited on the upper mother glass 1 having the red color filter R formed thereon. Then, the green resin is patterned by way of a photolithography and etching process. Consequently, a green color filter G is formed at the array region P1. A blue resin is deposited on the upper mother glass 1 having the green color filter G formed thereon. Then, the blue resin is patterned by way of a photolithography and etching process. Consequently, a blue color filter B is formed at the array region P1. Accordingly, the red, green and blue color filters 6 are formed at the array region P1, as shown in FIG. 3B.
As shown in FIG. 3C, the common electrode 10 is formed on an entire surface of the upper mother glass 1 having the red, green and blue color filters 6. Herein, in case of a liquid crystal display panel employing an IPS (In-Plane-Switching) mode, a planarization layer is formed on the upper mother glass 1 having the red, green and blue color filters 6.
The upper mother glass 1 having the color filter arrays 80 thereon is combined with the lower mother glass having the thin film transistor arrays thereon. After that, a scribing process is carried out to form a plurality of liquid crystal display panels.
Liquid crystal display panels formed by the process described above suffer from deterioration in that the color depth from one liquid crystal display panel to the next is not uniform. The non-uniformity is caused by thickness differences in the color filters 6 of the liquid crystal display panels, which results in uneven brightness.
More specifically, the color resin, for example, the red resin, is formed by a spinless coating method on the entire surface of the upper mother glass 1. As shown in FIG. 4A, the upper mother glass 1 is accommodated in a transferal cassette 77 and then transferred to a mask developing process. When the upper mother glass 1 is positioned in the cassette 77, the middle of the upper mother glass 1 sags as shown in FIG. 4B. As described above, when the middle of the upper mother glass 1 sags, some of the color resins at the edge of the upper mother glass 1 runs from the edge to the middle. As a result, a color resin that is thicker by a thickness d1 is formed in the middle of the upper mother glass 1. Since the resin that is patterned during the developing process also has an uneven thickness, the color filters 6 formed in the middle of the upper mother glass 1 have a greater thickness relative to the color filters 6 formed at the edge of the upper mother glass 1. As a result, the color depth between the liquid crystal display panels formed by the scribing process is not uniform and, in addition, the color depth in each of the liquid crystal display panels is not uniform. In other words, the thickness of the color filters 6 is uneven, which makes the light transmittance characteristics of the light source different. Accordingly, the color characteristics deteriorate such as the color depth of a picture represented between the liquid crystal display panels is not uniform, and the brightness is uneven due to the uneven transmittance. Especially in the case of a liquid crystal display panels employing an IPS mode, the above-mentioned problems affect the uniformity of the planarization layer formed on the color filters 6 causing the brightness to be uneven.